Intercommunication apparatus



June 1956 R. H. CAMPBELL INTERCOMMUNICATION APPARATUS Filed June 30, 1952 o A Wa Tmm IN V EN TOR. R/CHA R0 H. CAMPBEZL ATTORNEYS United States Patent INTERCOMIVIUNICATION APPARATUS Richard H. Campbell, Racine, Wis., assignor to Webster Electric Company, Racine, Wis., a corporation of Delaware Application June 30, 1952, Serial No. 296,415

7 Claims. (Cl. 17938) The present invention relates to intercommunication systems, and particularly to intercommunication systems of the loudspeaking type wherein a number of stations comprising the system are each provided with a loudspeaker type receiver, a microphone, and an amplifier so constructed and arranged that two-way communication over separate interstation circuits may be carried on without manipulation of switches.

The present invention has for one of its objects the provision of the system of the character set forth in the preceding paragraph with means for changing the character of the system for operation under different conditions and also providing a simplified arrangement for increasing the life of the amplifier tubes and components.

A further object of the present invention is to provide a new and improved two-way loudspeaking intercommunicating system with switch means movable between a plurality of positions, in one of which two-way communication over separate interstation circuits can be carried on without the manipulation of any talk-listen switches, in a second of which outgoing calls can be sent out at higher volume, and in a third of which incoming calls can be heard at higher volume.

A further object of the present invention is to provide a new and improved arrangement as set forth in the preceding paragraph wherein the plate voltage supply to the amplifier is also controlled by the plural position switch means and in which the plate supply is cut off in the third position of the switch means, i. e., when incoming calls are received at high volume.

A still further object of the present invention is to provide a two-way loudspeaking intercommunicating system including multi-position switch means of the character set forth above wherein said switch means is utilized also to control busy signal circuits.

Other objects and advantages of the present invention will become apparent from the ensuing description of an illustrative embodiment of the invention in the course of which reference is had to the accompanying drawing, the single figure of which is a schematic representation of a system embodying the invention.

Referring now to the drawing, the communication systern illustrated therein is shown to consist of two stations, namely stations 1 and 2. It should be understood that an actual installation will ordinarily consist of more stations which may be of the same type as stations 1 and 2 or of other types.

As heretofore indicated, the present invention relates primarily to systems wherein each of the stations is provided with an amplifier, a microphone, and a loudspeaker type receiver, and in which the microphone is connected directly to the input of the amplifier and the loudspeaker is supplied with amplified signal currents from other stations through an interstation circuit individual to the station. Thus, stations 1 and 2 are provided with the microphones 10 and 12, the loudspeaker type receivers 14 and 16, and the amplifiers 18 and 20, respectively.

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The amplifiers 18 and 20 are identical in construction and, inasmuch as they may be of well-known types, they have not been illustrated completely. It should perhaps be noted though that the microphones are each connected to a primary winding 22 of an input transformer and that each amplifier includes an output transformer 24 having input and output windings 26 and 28. The only other component shown is a cathode resistor 30 of an intermediate amplifier tube, which resistor is utilized for a purpose to be described shortly.

Each of the stations has what may be called a home line individual to it and an outgoing line adapted to be connected by suitable station selector means to desired called stations. The home line for station 1 includes the conductors 36 and 38, and the home line for station 2 includes the conductors 40 and 42. The station selector switches at station 1 are indicated generally by the reference character 44, and those at station 2 by the reference character 46.

In accordance with the present invention, each station is provided with auxiliary switch means 50 and 52 located at stations 1 and 2, respectively, which for convenience will be called high power switches, and providing a number of operating characteristics to be described shortly.

Loudspeaker 14 at station 1 has its voice coil 14-1 connected directly to conductor 38 and connectedto conductor 36 through reception volume control means comprising a fixed series resistor 54, and an adjustable series resistor 56 connected to a main volume control resistor 58 connected in turn across conductors 36 and 38. In similar manner the voice coil 16-1 of loudspeaker 16 at station 2 is connected to conductors 40 and 42. The connection to co'nductor 42 is direct while the connection to conductor 40 is through the fixed series resistor 64, the adjustable series resistor 66, and the resistor 68 connected across conductors 40 and 42.

The high power switches 50 and 52 are operable into a plurality of positions, namely three, in the illustrated arrangement. They are shown in what may be considered their normal up position from which they are movable into a central, horizontal position and to a third, down position. In the normal up position, incoming calls come in at high volume, in the center position talking and listening is carried on at a normal intermediate volume, while in the down position outgoing calls are transmitted at maximum volume.

The volume of the incoming calls is controlled through the series resistors 54 and 56 and 64 and 66 at the respective station; the volume of the outgoing signals being controlled by controlling the gain of the associated amplifier; the arrangement being also such that the high power switch completes the plate voltage circuit of the amplifier only in the central and down positions. In accordance with a further feature of the invention, the high power switches are also utilized to control the busy signal circuits of the system.

The high power switches include five three-position switch blades indicated by the suflixes 1 to 5. Inasmuch as the circuit arrangements at stations 1 and 2 are identical, the detailed description of the apparatus at station 1 only will be given, the corresponding equipment at the two stations being indicated by the individual reference character followed by the suffixes 1 and 2 for the two stations.

In the normal indicated up position of high power switch 50 at station 1, the busy signal circuit controlling switch blade 50-1 disconnects circuit 36, 38 individual to station 1 from ground, the ground circuit 70-1 being connected only to the two lower stationary contacts of the switch while the switch blade itself is connected by conductor 72-1 to the junction of the balanced resistors 74-1 and 76-1 which are in turn connected across the station l'h'omelin'e.

In the up position, a reception volume controlling switch blade 50-2 short circuits the series resistors 54 and '56, this being done through conductors 73-1 and 86-1. In this up position a second reception volume controlling switch blade 50-3 is in open circuit position.

In the normal up position, the amplifier plate voltage supply circuit is broken by the switch blade 50-4 which is in open circuit position. It may be well to note at this point that the switch blade is connected by conductor 82-1 to the amplifier plate circuit, while the two stationary contacts are connected by conductor 84-1 to a conductor 86-1 to the indicated plate voltage supply (B+).

In the normal up position, the amplifier gain controlling switch blade 50-5 controlling the volume of transmitted messages is in open circuit position. It should perhaps be noted at this point that the gain of the amplifier is controlled through control of the inverse feedback of the amplifier. 'To control the inverse feedback, the switch blade '50-5 is connected by conductor 88-1 to the cathode resistor 30 while the lower stationary contacts are connected to the primary 26 of the output transformer .24 through conductor 90-1, a capacitor 92-1, and conductor 94-1. The latter leads directly to the central contact associated with switch blade 50-5 while a feedback descreasing resistor 96-1 is interposed between conductor 94-1 and the lowermost contact associated with the switch blade.

The busy signalling means at the two stations are identical and in the further description thereof the apparatus at the two stations will be indicated by the use of suflixes as in the earlier description. The busy signalling means includes a normally energized relay 100-1 having an operating winding 102-1 and a movable switch blade 104-1 controlling the supply of power to a pilot light 106-1 connected to the secondary winding 108-1 of a small power transformer having a primary winding 110-1. The amount of energy supplied to the pilot light is controlled by resistor 111-1 which is selectively short circuited by switch blade 104-1 through conductors 112-1 and 114-1. Therelay winding 102-1 is connected through resistor 116-1 to the plate voltage supply conductor 86-1 and to ground through conductor 118-1. It is also connected by conductor 120-1 to the junction of balanced resistors 122-1 and 124-1 connected across the conductors 126-1 and 128-1"constituting the outgoing lines from station number 1 and which are connected to the secondary winding 28 of output transformer 24.

The outgoing lines 126-1 and 128-1 are connected to a station selector switch 44-2 through which station 1 selects station 2 for calling. Other station selector switches such as 44-3 may be provided so that other stations in the system (not shown) may be selected. In similar manner station selector 46 at station 2 has a selector switch 46-1 for the selection of station 1 and a switch 46-3 for the selection of another station (not shown). The busy signalling arrangement is such that relay 100 completes a short circuit across resistor 111-1 in the normal idle condition of a station and also when a nonbusy station is selected. However, when a busy station is selected, the relay is connected to ground through the selected interstation circuit and the busy signal control means at another station (such as 52-1 at station 2 and corresponding means at other stations, not shown) whereupon the flow of current to the relay decreases to such a value that the switch blade 104-1 opens to place resistor 111-1 in series with the pilot light and to decrease the flow of current to the pilot light and provide an indication that the selected station is busy.

To initiate a call, for example, at station 1, the high power switch 50 is moved either to its central or lower position. Normally it would be moved only to its central position. When this is done, the amplifier is supplied with jplat'e voltage and thus rendered immediately operative. Also, the desired station selector switch is closed, and, in this case it is assumed that the switch 44-1 is closed so that station 2 can be called by amplified voice signals. Assuming that switch 50 is moved to its central position, then the various switch blades efiect the following operations. Switch blade 50-1 grounds the home line for station 1 'so that any other station selecting it will be given a busy signal in amanner-described above, i. e., by grounding of the relay winding 102 at the selecting station. The switch blade 50-2 removes the short circuit from around both series resistors 54 and 56 but still short circuits resistor 56 through conductors 78-1 and 130-1. Switch blade 50-3 places resistor 132-1 in parallel with the voice coil 14-1 through conductors -1 and 134-1. The switch blade 50-4 completes the plate voltage supply circuit in a manner described heretofor and switch blade 50-5 connects conductors 94-1 and 88-1 thereby to provide a maximum feedback to decrease the amplifier gain to a desired value.

When station 2 responds to the call, the selector switch 46-2 thereat is closed and the .high power switch 52 is operated .to a central position so that apparatus at both stations is in the same condition. When station .2 does operate its switch, then the busy signal circuits for both stations are completed and the pilot lights thereat are supplied with less energy and glow with decreased brilliancy. Also, those at any other station selecting either station 1 or station 2 would be supplied with less energy to indicate that stations 1 or 2 are'busy.

In the event there should be an excessive amount of noise at one of the stations, the operator at the other station can operate his high power switch to send the message to the station at higher volume. Assuming that station 2 is at a noisy location, then the operator at station 1 can increase the volume of signals sent to station 2 by operating switch 50 to its lowermost position. In the event this is done, switch blade 50-1 continues to connect station 1 home line to ground; switch blade 50-2 moves to a circuit opening position thereby inserting resistor 56 inseries with a loudspeaker to decrease the .incoming signal to station 1; switch blade 50-3 continues to connect resistor 132-1 in parallel with the voice coil of loudspeaker 14; switch blade 50-4 continues to complete the amplifier B supply; and switch blade 50-5 supplies a decreased amount of inverse feedback through resistor 96-1. Thus, the gain of amplifier 18 at station 1 is increased so that signals sent from station 1 to station 2 are sent at greater volume. At the same time the acoustic feedback between the two channels remains at the same value by reason of the simultaneous decrease in the listening volume at station 1.

Should both stations be located at noisy positions, the switches 50 and 52 can be alternately operated so that the transmitted messages are transmitted at higher volume.

While the present invention has been described in connection with an alternative embodiment, it should be apparent to those skilled in the art that the principles thereof are not limited to the details of the embodiment described;

What I claim as new and desire to secure by United 'States Letters Patent is:

1. In an intercomrnunication system, the combination including, a plurality of stations, separate voice receiving and transmitting means at each station, an amplifier at each station, a source of plate voltage for each amplifier, the transmitting means at each station being permanently connected to the input of the amplifier, interstation communication circuits between stations, the receiving means at each station being connected to an interstation circuit individual to the station, each amplifier including amplifier gain control means, reception volume control means for controlling said amplifier gain control means, reception volume control means and the connections of the amplifier to the plate voltage source, said plural position control means in one position breaking the plate voltage supply circuit and conditioning said reception volume control means for reception at maximum volume; in a second position completing the plate voltage supply circuit for the amplifier, conditioning the amplifier for operation at minimum gain and said reception means for reception at an intermediate volume, and in a third position conditioning said amplifier for operation at maximum gain, completing the plate voltage supply circuit, and conditioning said receiving means for reception at minimum volume.

2. An intercommunication unit, including in combination, voice receiving and transmitting means, an amplifier, a source of plate voltage for the amplifier, the transmitting means being permanently connected to the input of the amplifier, an incoming circuit, the receiving means being connected to said circuit, said amplifier including amplifier gain control means, and reception volume control means for the receiving means, and means including plural position amplifier gain, reception volume and plate voltage supply control means for controlling said amplifier gain control means, reception volume control means and the connections of the amplifier to the plate voltage source, said plural position control means in one position breaking the plate voltage supply circuit and conditioning said reception volume control means for reception at maximum volume; in a second position completing the plate voltage supply circuit for the amplifier, conditioning the amplifier for operation at minimum gain and said reception means for reception at an intermediate volume; and in a third position conditioning said amplifier for operation at maximum gain, completing the plate voltage supply circuit, and conditioning said receiving means for reception at minimum volume.

3. In an intercommunication system, the combination including, a plurality of stations, separate receiving and transmitting means at each station, an amplifier at each station, the transmiting means a each station being permanently connected to the input of the amplifier, interstation communication circuits between stations, the receiving means at each station being connected to an interstation circuit individual to the station, each amplifier including amplifier gain control means, reception volume control means for the receiving means at each station, and means including plural position amplifier gain and reception volume control means at each station for controlling said amplifier gain control means and reception volume control means, said plural position control means in one position conditioning said reception volume control means for reception at maximum volume; in a second position conditioning the amplifier for operation at minimum gain and said reception means for reception at an intermediate volume; and in a third position conditioning said amplifier for operation at maximum gain and said receiving means for reception at minimum volume.

4. An intercommunication unit, including in combination, receiving and transmitting means, an amplifier, the transmitting means being permanently connected to the input of the amplifier, an incoming circuit, the receiving means being connected to said circuit, said amplifier including amplifier gain control means, reception volume control means for the receiving means, and means including plural position amplifier gain and reception volume control means for controlling said amplifier gain control means and reception volume control means, said plural position control means in one position conditioning said reception volume control means for reception at maximum volume; in a second position conditioning the amplifier for operation at minimum gain and said reception means for reception at an intermediate volume; and in a third position conditioning said amplifier for operation at maximum gain and said receiving means for reception at minimum volume.

5. In an intercommunication system, the combination including, a plurality of stations, receiving and transmitting means at each station, the receiving means being connected to an interstation circuit, amplifier means at each station having an output circuit, means including selector switch means for connecting the output circuit to interstation circuits individual to other stations, reception and amplifier gain control means at each station for the receiving means and amplifier thereat, means including plural position switch means operatively connected to and controlling both said last-mentioned means, and busy signal means at each station including a pair of balanced resistors connected to said interstation circuit and another pair to the output circuit, a relay connected between said other pair and ground, a ground circuit, and other switch means operatively connected to and operable simultaneously with said plural position switch means for connecting said first pair of resistors to said ground circuit.

6. In an intercommunication system, the combination including, 'a plurality of stations, interstation circuits between stations, voice receiving and transmitting means at each station connected to said circuits, an amplifier at each station connected to the transmitting means thereat, and means including plural position switch means at each station for controlling the amplifier gain and reception volume, said switch means being operable into first positions in which they condition the receiving means for reception at high volume and render the amplifier means inoperative, to second positions wherein they condition the receiving means for reception at minimum volume and the amplifier means for transmission at high volume, and to third positions wherein they condition the receiving means for reception at intermediate volume, and the amplifier means for transmission at low volume.

7. An intercommunication unit, including in combination, voice receiving and transmitting means, an amplifier connected to said transmitting means and including gain control means, reception volume control means associated with said receiving means, and means including plural position switch means for controlling the amplifier gain control means and reception volume control means, said switch means being operable into a first position in which it conditions the receiving means for reception at high volume and renders the amplifier inoperative, to a second position wherein it conditions the receiving means for reception at minimum volume and the amplifier for transmission at high volume, and to a third position wherein it conditions the receiving means for reception at intermediate volume and the amplifier for transmission at low volume.

References Cited in the file of this patent UNITED STATES PATENTS 2,269,141 Campbell Jan. 6, 1942 2,269,143 Campbell Ian. 6, 1942 2,269,144 Campbell Jan. 6, 1942 2,323,307 Campbell July 6, 1943 2,529,912 Campbell Nov. 14, 1950 

